| Aug. 21, 2008: Nilanthi successfully defends her PhD dissertation. |
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N. Warnasooriya, “Quantitative phase imaging microscopy with multi-wavelength optical phase unwrapping”
This dissertation presents a quantitative phase imaging microscopy technique that combines phase-shifting interferometry with multi-wavelength optical phase unwrapping.
The technique consists of a Michelson-type interferometer illuminated with any of three types of light sources; light emitting diodes, laser diodes and a ring dye laser. Interference
images are obtained by using a 4-frame phase shifting method, and are combined to calculate the phase of the object surface. The 2π ambiguities are removed by repeating
the experiment combining two and three different wavelengths, which yields phase images of effective wavelength much longer than the original. The resulting image is a
profile of the object surface with a height resolution of several nanometers and range of several microns. To our knowledge, this is the first time that a three wavelength optical
phase unwrapping method with no amplified phase noise has been presented for full frame phase images.
The results presented here are divided into three main categories based on the source of illumination; light emitting diodes, laser diodes and a ring dye laser. Results for
both two-wavelength optical unwrapping and three-wavelength optical unwrapping techniques are demonstrated.
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The interferographic images using broadband sources such as light emitting diodes are significantly less affected by coherent noise compared to images obtained
using lasers. Our results show that the three wavelength optical phase unwrapping can also be effectively applied to unwrap phase images obtained using coherent light sources
such as lasers and laser diodes, without amplifying phase noise in the final phase image. We have successfully shown that our multi-wavelength phase-shifting technique
extends the range free of 2π ambiguities in the phase map without using conventional computation intensive phase unwrapping methods. This phase imaging technique can be
used to measure physical thickness or height of both biological and other microscopic samples, with nanometer axial resolution. An added advantage of the multi-wavelength
optical phase unwrapping technique is that the beat wavelength can be tailored to match height variations of specific samples.
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REU oral presentation
Group Photo with Chair Yoshikawa
Graduate students Lee and Jeong from Yonsei University in Seoul, Korea begin a two week long visit to DHML to explore digital holography and collaborative research opportunities. Pictured here, the group enjoys a delicious sushi dinner before saying good-bye.
Dr. Kim is honored as a recent OSA Fellow while David presents his paper entitled 
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